Dale Cherne Wrote:
-------------------------------------------------------
> Tom,
>
> What about the Western Maryland 162 ton Shay ("Big
> 6") up in Cass Scenic Railway? How do those
> cylinders compare with the #91 cylinder volume?

. And yes, you're absolutely right
> about the superheaters. Forgot that they just
> pre-heat the water. None of the Shays had them
> from what I read. The Willamette's had them
> though.

Just out of curiosity Tom, I have noticed
> that #91 is pretty fast on her feet for a Heisler.
> I'm guessing its around 25mph?


IIRC, the cylinders on the WM Shay are 17" by 18"...huge. This Shay also has much larger
drivers, 48", I think, vs. 36" found on most 3T Shays.

Not sure of what you are talking about regarding Superheaters...they have nothing to do
with preheating water. That is what a Feedwater Heater does, uses some of the heat that
would otherwise go up the stack as waste and uses it to raise the temperature of the boiler
feedwater, thus lessening the amount of fuel needed.
The Superheater takes Saturated steam & raises its temperature. In so doing, for a given
amount of water, say one pound, the volume of steam increases and it is able to do more
work.
When you say that none of the Shays had them, what are you referring to? And the
Willamette locomotive did? If you'll be more specific here, I can try to help.

About the Heisler being fast, as a generality, they are a faster road engine than a Shay
or Climax and 2:1 gearing was pretty common on some of the 3T models. This with larger
diameter drivers than a Shay made them a little faster. I think that the 91 gets some of
higher tractive effort from more than the quarter inch bigger bore on the cylinders and
the 200 lbs. boiler pressure. Have not counted the teeth on her ring & pinion, but I'd
bet a beer that the gear ratio is lower than 2:1 and that would account for the higher
tractive effort that the machine has compared to other 3T Heislers.
Not for me to say, but I'd venture that the 91 is maybe comfortable around 20 mph without
beating her...much faster than that most likely increases maintenance and failures. This
is all assuming that she is in good mechanical shape and not worn needing shopping.